Memory cells, methods of fabrication, and semiconductor devices

ABSTRACT

A magnetic cell includes a magnetic tunnel junction that comprises magnetic and nonmagnetic materials exhibiting hexagonal crystal structures. The hexagonal crystal structure is enabled by a seed material, proximate to the magnetic tunnel junction, that exhibits a hexagonal crystal structure matching the hexagonal crystal structure of the adjoining magnetic material of the magnetic tunnel junction. In some embodiments, the seed material is formed adjacent to an amorphous foundation material that enables the seed material to be formed at the hexagonal crystal structure. In some embodiments, the magnetic cell includes hexagonal cobalt (h-Co) free and fixed regions and a hexagonal boron nitride (h-BN) tunnel barrier region with a hexagonal zinc (h-Zn) seed region adjacent the h-Co. The structure of the magnetic cell enables high tunnel magnetoresistance, high magnetic anisotropy strength, and low damping. Methods of fabrication and semiconductor devices are also disclosed.

TECHNICAL FIELD

The present disclosure, in various embodiments, relates generally to thefield of memory device design and fabrication. More particularly, thisdisclosure relates to design and fabrication of memory cellscharacterized as spin torque transfer magnetic random access memory(STT-MRAM) cells, which may be otherwise known in the art asspin-transfer torque random-access memory (STT-RAM) cells.

BACKGROUND

Magnetic Random Access Memory (MRAM) is a non-volatile computer memorytechnology based on magnetoresistance. One type of MRAM cell is a spintorque transfer MRAM (STT-MRAM) cell, which includes a magnetic cellcore supported by a substrate. The magnetic cell core includes amagnetic tunnel junction (“MTJ”) having at least two magnetic regions,for example, a “fixed region” and a “free region,” with a nonmagnetic,“tunnel” region between. The free region and the fixed region mayexhibit magnetic orientations that are either horizontally oriented(“in-plane”) or perpendicularly oriented (“out-of-plane”) relative tothe width of the regions. The fixed region includes a magnetic materialthat has a substantially fixed (e.g., a non-switchable) magneticorientation. The free region, on the other hand, includes a magneticmaterial that has a magnetic orientation that may be switched, duringoperation of the cell, between a “parallel” configuration and an“anti-parallel” configuration. In the parallel configuration, themagnetic orientations of the fixed region and the free region aredirected in the same direction (e.g., north and north, east and east,south and south, or west and west, respectively). In the “anti-parallel”configuration, the magnetic orientations of the fixed region and thefree region are directed in opposite directions (e.g., north and south,east and west, south and north, or west and east, respectively). In theparallel configuration, the STT-MRAM cell exhibits a lower electricalresistance across the magnetoresistive elements (e.g., the fixed regionand free region). This state of low electrical resistance may be definedas a “0” logic state of the MRAM cell. In the anti-parallelconfiguration, the STT-MRAM cell exhibits a higher electrical resistanceacross the magnetoresistive elements. This state of high electricalresistance may be defined as a “1” logic state of the STT-MRAM cell.

Switching of the magnetic orientation of the free region may beaccomplished by passing a programming current through the magnetic cellcore and the fixed and free regions therein. The fixed region polarizesthe electron spin of the programming current, and torque is created asthe spin-polarized current passes through the core. The spin-polarizedelectron current exerts the torque on the free region. When the torqueof the spin-polarized electron current passing through the core isgreater than a critical switching current density (J_(c)) of the freeregion, the direction of the magnetic orientation of the free region isswitched. Thus, the programming current can be used to alter theelectrical resistance across the magnetic regions. The resulting high orlow electrical resistance states across the magnetoresistive elementsenable the write and read operations of the STT-MRAM cell. Afterswitching the magnetic orientation of the free region to achieve the oneof the parallel configuration and the anti-parallel configurationassociated with a desired logic state, the magnetic orientation of thefree region is usually desired to be maintained, during a “storage”stage, until the STT-MRAM cell is to be rewritten to a differentconfiguration (i.e., to a different logic state).

Beneficial properties of free regions are often associated with themicrostructure of the free regions. These properties include, forexample, the cell's tunnel magnetoresistance (“TMR”). TMR is a ratio ofthe difference between the cell's electrical resistance in theanti-parallel configuration (R_(ap)) and its resistance in the parallelconfiguration (R_(p)) to R_(p) (i.e., TMR=(R_(ap)−R_(p))/R_(p)).Generally, a free region with a consistent crystal structure having fewstructural defects in the microstructure of its magnetic material has ahigher TMR than a thin free region with structural defects. A cell withhigh TMR may have a high read-out signal, which may speed the reading ofthe STT-MRAM cell during operation. High TMR may also enable use of lowprogramming current.

Efforts have been made to form magnetic memory cells havingmicrostructures that are conducive for high TMR. However, selectingmaterials for and designing conventional magnetic memory cells with highTMR has presented challenges. For example, forming conventional magneticmaterials with consistent, crystal microstructures has presentedchallenges at least because of differing magnetic structures in the MTJand other regions of the memory cell. Efforts to improve crystallizationin the MTJ have included formulating magnetic materials to initiallyinclude additives that enable the magnetic material to be formed in aninitial, amorphous state, so that a desired crystal structure may laterbe propagated to the magnetic material as the additive is diffused outof the magnetic material. However, the diffusing additive can interferewith other materials and degrade other properties of the magnetic cell(e.g., magnetic anisotropy (“MA”) strength, TMR). Therefore, formulatingmaterials for and designing structures of magnetic memory cells toachieve high TMR, while not affecting other characteristics of the cell,such as MA strength, can present challenges.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional, elevational, schematic illustration of amagnetic tunnel junction (“MTJ”) of a magnetic cell core, according toan embodiment of the present disclosure.

FIG. 1A is a cross-sectional, elevational, schematic illustration of theMTJ of FIG. 1, according to an embodiment of the present disclosure,wherein a free region and a fixed region exhibit out-of-plane magneticorientations.

FIG. 1B is a cross-sectional, elevational, schematic illustration of theMTJ of FIG. 1, according to an embodiment of the present disclosure,wherein a free region and a fixed region exhibit in-plane magneticorientations.

FIG. 2 is a view of box 2 of FIG. 1, illustrating, in simplified form,the microstructural alignment of the materials of the MTJ of FIG. 1.

FIG. 3 is a cross-sectional, elevational, schematic illustration of amagnetic cell structure according to an embodiment of the presentdisclosure, wherein the magnetic cell structure is configured as atop-pinned magnetic memory cell and includes a single seed regionunderlying an MTJ.

FIG. 4 is a cross-sectional, elevational, schematic illustration of amagnetic cell structure according to an embodiment of the presentdisclosure, wherein the magnetic cell structure is configured as abottom-pinned magnetic memory cell and includes a single seed regionunderlying an MTJ.

FIG. 5 is a cross-sectional, elevational, schematic illustration of amagnetic cell structure according to an embodiment of the presentdisclosure, wherein the magnetic cell structure is configured as atop-pinned magnetic memory cell and includes a single seed regionoverlying an MTJ.

FIG. 6 is a cross-sectional, elevational, schematic illustration of amagnetic cell structure according to an embodiment of the presentdisclosure, wherein the magnetic cell structure is configured as abottom-pinned magnetic memory cell and includes a single seed regionoverlying an MTJ.

FIG. 7 is a cross-sectional, elevational, schematic illustration of amagnetic cell structure according to an embodiment of the presentdisclosure, wherein the magnetic cell structure is configured as atop-pinned magnetic memory cell and includes dual seed regions, oneoverlying an MTJ and another underlying the MTJ.

FIG. 8 is a cross-sectional, elevational, schematic illustration of amagnetic cell structure according to an embodiment of the presentdisclosure, wherein the magnetic cell structure is configured as abottom-pinned magnetic memory cell and includes dual seed regions, oneoverlying an MTJ and another underlying the MTJ.

FIG. 9 is a cross-sectional, elevational, schematic illustration of astage of processing to fabricate the magnetic cell structure of FIG. 1,according to an embodiment of the present disclosure.

FIG. 10 is a schematic diagram of an STT-MRAM system including a memorycell having a magnetic cell structure according to an embodiment of thepresent disclosure.

FIG. 11 is a simplified block diagram of a semiconductor devicestructure including memory cells having a magnetic cell structureaccording to an embodiment of the present disclosure.

FIG. 12 is a simplified block diagram of a system implemented accordingto one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

Memory cells, semiconductor devices, memory systems, electronic systems,and methods of forming memory cells are disclosed. The memory cellsinclude a magnetic tunnel junction (“MTJ”) comprising a pair of magneticregions on opposite sides of a nonmagnetic, tunnel barrier region. Eachof the magnetic regions and the nonmagnetic tunnel barrier regionexhibit a hexagonal crystal structure, and the materials of the MTJ forma microstructure with the crystalline structures of each materialoriented relative to one another in what is characterized herein as an“aligned lattice microstructure,” i.e., a crystal structure in which thecrystal structures of adjoining, different materials interface in asubstantially-consistent, repeating pattern. To enable formation of thehexagonal crystal structure of each material and the aligned latticemicrostructure of the MTJ, the MTJ is disposed proximate to a seedregion that exhibits the desired hexagonal crystal structure. Thehexagonal crystal structure of the seed region either effects thehexagonal crystal structure of the materials of the MTJ as the materialsare formed over the seed region, or, alternatively, the hexagonalcrystal structure of the seed region is propagated to the materials ofthe MTJ after precursor materials of the MTJ are formed. In any case,the resulting MTJ includes a substantially aligned, consistent (i.e.,substantially defect-free) microstructural lattice with hexagonalcrystal materials. Such an aligned MTJ structure may exhibit a hightunnel magnetoresistance (“TMR”) and a high magnetic anisotropy (“MA”).

As used herein, the terms “high tunnel magnetoresistance” and “high TMR”mean and refer to a TMR greater than about 2.00 (200%).

As used herein, the terms “high magnetic anisotropy” and “high MA,” meanand refer to MA strength greater than about 1,000 Oersted.

As used herein, the term “substrate” means and includes a base materialor other construction upon which components, such as those within memorycells, are formed. The substrate may be a semiconductor substrate, abase semiconductor material on a supporting structure, a metalelectrode, or a semiconductor substrate having one or more materials,structures, or regions formed thereon. The substrate may be aconventional silicon substrate or other bulk substrate including asemiconductive material. As used herein, the term “bulk substrate” meansand includes not only silicon wafers, but also silicon-on-insulator(“SOI”) substrates, such as silicon-on-sapphire (“SOS”) substrates orsilicon-on-glass (“SOG”) substrates, epitaxial layers of silicon on abase semiconductor foundation, or other semiconductor or optoelectronicmaterials, such as silicon-germanium (Si_(1-x)Ge_(x), where x is, forexample, a mole fraction between 0.2 and 0.8), germanium (Ge), galliumarsenide (GaAs), gallium nitride (GaN), or indium phosphide (InP), amongothers. Furthermore, when reference is made to a “substrate” in thefollowing description, previous process stages may have been utilized toform materials, regions, or junctions in the base semiconductorstructure or foundation.

As used herein, the term “STT-MRAM cell” means and includes a magneticcell structure that includes a magnetic cell core including an MTJ. TheMTJ includes a nonmagnetic, “tunnel barrier” region disposed between twomagnetic regions, i.e., a free region and a fixed region. Thenonmagnetic tunnel barrier region may be an electrically insulative(e.g., dielectric) region.

As used herein, the terms “magnetic cell core” means and includes amemory cell structure comprising the free region and the fixed regionand through which, during use and operation of the memory cell, currentmay be passed (i.e., flowed) to effect a parallel or anti-parallelconfiguration of the magnetic orientations of the free region and thefixed region.

As used herein, the term “magnetic region” means a region that exhibitsmagnetism. A magnetic region includes a magnetic material and may alsoinclude one or more nonmagnetic materials.

As used herein, the term “magnetic material” means and includesferromagnetic materials, ferrimagnetic materials, antiferromagnetic, andparamagnetic materials.

As used herein, the term “coupler,” when referring to a material,region, or sub-region, means and includes a material, region, orsub-region formulated or otherwise configured to antiferromagneticallycouple neighboring magnetic materials, regions, or sub-regions.

As used herein, the term “precursor,” when referring to a material orstructure, means and refers to a material or structure to be transformedinto a resulting material or structure. For example, and withoutlimitation, a “precursor material” may refer to a material having aninitial microstructure (e.g., an amorphous structure) that is to beconverted into a different, final microstructure (e.g., a crystalstructure), and “a precursor structure” may refer to a structure ofmaterials or regions to be patterned to transform the precursorstructure into a resulting, patterned structure (e.g., a magnetic cellstructure).

As used herein, the term “to template,” means and refers to the act ofone material orienting its crystal structure to the crystal structure ofanother material during fabrication of the one material such that thetwo materials have matching crystal structures.

As used herein, the term “matching,” when used to compare one material'scrystal structure to the crystal structure of another adjoiningmaterial, means and refers to the two materials having, at least alongan interface between the two materials, crystal structures classified inthe same geometric crystal system (e.g., both hexagonal, both cubic) andsimilar lattice lengths of the material's unit cell face directed towardthe interface. As used herein, “similar lattice lengths” mean and referto lattice lengths differing, if at all, by less than about 10% (e.g.,less than about 6%, e.g., less than about 5%). For example and withoutlimitation, “matching” crystal structures may include two hexagonalcrystal structures adjoining one another along an interface with thebasal (i.e., hexagon-shaped) face of each directed toward the other andwith an a-axis lattice length that differs by less than about 10%. Thec-axis lattice lengths of the crystal structures (i.e., the heights ofthe prismatic faces) may nonetheless differ by more or less than about10% with the crystal structures nonetheless referred to herein as“matching.”

As used herein, the term “hexagonal crystal structure,” means and refersto a crystal structure defined by at least one hexagonal face.

As used herein, unless the context indicates otherwise, the term “formedfrom,” when describing a material or region, refers to a material orregion that has resulted from an act that produced a transformation of aprecursor material or precursor region.

As used herein, the term “fixed region” means and includes a magneticregion within the STT-MRAM cell that includes a magnetic material andthat has a fixed, or substantially fixed, magnetic orientation duringuse and operation of the STT-MRAM cell in that a current or appliedfield effecting a change in the magnetization direction of one magneticregion (e.g., the free region) of the cell core may not effect a changein the magnetization direction of the fixed region. The fixed region mayinclude one or more magnetic materials and, optionally, one or morenonmagnetic materials. For example, the fixed region may include asynthetic antiferromagnet (SAF) including a coupler sub-region ofruthenium (Ru) adjoined by alternating sub-regions of magnetic andconductive materials. Alternatively, the fixed region may includestructures of alternating sub-regions of magnetic material and couplermaterial. Each of the magnetic sub-regions may include one or morematerials and one or more sub-regions therein. As another example, thefixed region may be configured as a single, homogeneous, magneticmaterial. Accordingly, the fixed region may have uniform magnetizationor sub-regions of differing magnetization that, overall, effect thefixed region having a fixed, or substantially fixed, magneticorientation during use and operation of the STT-MRAM cell.

As used herein, the term “free region” means and includes a magneticregion within the STT-MRAM cell that includes a magnetic material andthat has a switchable magnetic orientation during use and operation ofthe STT-MRAM cell. The magnetic orientation may be switched between aparallel configuration and an anti-parallel configuration by theapplication of a current or applied field.

As used herein, “switching” means and includes a stage of use andoperation of the memory cell during which programming current is passedthrough the magnetic cell core of the STT-MRAM cell to effect a parallelor anti-parallel configuration of the magnetic orientations of the freeregion and the fixed region.

As used herein, “storage” means and includes a stage of use andoperation of the memory cell during which programming current is notpassed through the magnetic cell core of the STT-MRAM cell and in whichthe parallel or anti-parallel configuration of the magnetic orientationsof the free region and the fixed region is not purposefully altered.

As used herein, the term “vertical” means and includes a direction thatis perpendicular to the width and length of the respective region.“Vertical” may also mean and include a direction that is perpendicularto a primary surface of the substrate on which the STT-MRAM cell islocated.

As used herein, the term “horizontal” means and includes a directionthat is parallel to at least one of the width and length of therespective region. “Horizontal” may also mean and include a directionthat is parallel to a primary surface of the substrate on which theSTT-MRAM cell is located.

As used herein, the term “sub-region,” means and includes a regionincluded in another region. Thus, one magnetic region may include one ormore magnetic sub-regions, i.e., sub-regions of magnetic material, aswell as nonmagnetic sub-regions, i.e., sub-regions of nonmagneticmaterial.

As used herein, the term “between” is a spatially relative term used todescribe the relative disposition of one material, region, or sub-regionrelative to at least two other materials, regions, or sub-regions. Theterm “between” can encompass both a disposition of one material, region,or sub-region directly adjacent to the other materials, regions, orsub-regions and a disposition of one material, region, or sub-regionindirectly adjacent to the other materials, regions, or sub-regions.

As used herein, the term “proximate to” is a spatially relative termused to describe disposition of one material, region, or sub-region nearto another material, region, or sub-region. The term “proximate”includes dispositions of indirectly adjacent to, directly adjacent to,and internal to.

As used herein, reference to an element as being “on” or “over” anotherelement means and includes the element being directly on top of,adjacent to, underneath, or in direct contact with the other element. Italso includes the element being indirectly on top of, adjacent to,underneath, or near the other element, with other elements presenttherebetween. In contrast, when an element is referred to as being“directly on” or “directly adjacent to” another element, there are nointervening elements present.

As used herein, other spatially relative terms, such as “below,”“lower,” “bottom,” “above,” “upper,” “top,” and the like, may be usedfor ease of description to describe one element's or feature'srelationship to another element(s) or feature(s) as illustrated in thefigures. Unless otherwise specified, the spatially relative terms areintended to encompass different orientations of the materials inaddition to the orientation as depicted in the figures. For example, ifmaterials in the figures are inverted, elements described as “below” or“under” or “on bottom of” other elements or features would then beoriented “above” or “on top of” the other elements or features. Thus,the term “below” can encompass both an orientation of above and below,depending on the context in which the term is used, which will beevident to one of ordinary skill in the art. The materials may beotherwise oriented (rotated 90 degrees, inverted, etc.) and thespatially relative descriptors used herein interpreted accordingly.

As used herein, the teens “comprises,” “comprising,” “includes,” and/or“including” specify the presence of stated features, regions, stages,operations, elements, materials, components, and/or groups, but do notpreclude the presence or addition of one or more other features,regions, stages, operations, elements, materials, components, and/orgroups thereof.

As used herein, “and/or” includes any and all combinations of one ormore of the associated listed items.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

The illustrations presented herein are not meant to be actual views ofany particular material, species, structure, device, or system, but aremerely idealized representations that are employed to describeembodiments of the present disclosure.

Embodiments are described herein with reference to cross-sectionalillustrations that are schematic illustrations. Accordingly, variationsfrom the shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are to be expected. Thus,embodiments described herein are not to be construed as limited to theparticular shapes or regions as illustrated but may include deviationsin shapes that result, for example, from manufacturing techniques. Forexample, a region illustrated or described as box-shaped may have roughand/or nonlinear features. Moreover, sharp angles that are illustratedmay be rounded. Thus, the materials, features, and regions illustratedin the figures are schematic in nature and their shapes are not intendedto illustrate the precise shape of a material, feature, or region and donot limit the scope of the present claims.

The following description provides specific details, such as materialtypes and processing conditions, in order to provide a thoroughdescription of embodiments of the disclosed devices and methods.However, a person of ordinary skill in the art will understand that theembodiments of the devices and methods may be practiced withoutemploying these specific details. Indeed, the embodiments of the devicesand methods may be practiced in conjunction with conventionalsemiconductor fabrication techniques employed in the industry.

The fabrication processes described herein do not form a completeprocess flow for processing semiconductor device structures. Theremainder of the process flow is known to those of ordinary skill in theart. Accordingly, only the methods and semiconductor device structuresnecessary to understand embodiments of the present devices and methodsare described herein.

Unless the context indicates otherwise, the materials described hereinmay be formed by any suitable technique including, but not limited to,spin coating, blanket coating, chemical vapor deposition (“CVD”), atomiclayer deposition (“ALD”), plasma enhanced ALD, physical vapor deposition(“PVD”) (e.g., sputtering), laser ablation, or epitaxial growth.Depending on the specific material to be formed, the technique fordepositing or growing the material may be selected by a person ofordinary skill in the art.

Unless the context indicates otherwise, the removal of materialsdescribed herein may be accomplished by any suitable techniqueincluding, but not limited to, etching, ion milling, abrasiveplanarization, or other known methods.

Reference will now be made to the drawings, where like numerals refer tolike components throughout. The drawings are not necessarily drawn toscale.

A memory cell is disclosed. The memory cell includes a magnetic tunneljunction (“MTJ”) in a magnetic cell core. The MTJ includes anonmagnetic, tunnel barrier region between a magnetic region and anothermagnetic region. Each of the regions of the MTJ has a crystal structurethat effects a high tunnel magnetoresistance (TMR). The crystalstructure is enabled by the MTJ's proximity to a seed region thatexhibits the desired crystal structure.

With reference to FIG. 1, illustrated is an MTJ 100 of embodiments ofthe present disclosure. The MTJ 100 includes a magnetic region andanother magnetic region, for example, a “fixed region” 110 and a “freeregion” 120, respectively. A nonmagnetic “tunnel barrier region” 130 isdisposed between the two magnetic regions.

In some embodiments, each of the fixed region 110, the free region 120,and the tunnel barrier region 130 may have a thickness of about 0.25 nmto about 2 nm each, for a total thickness of the MTJ 100 of about 0.75nm to about 6 nm. For example, and without limitation, one or more ofthe fixed region 110, the free region 120, and the tunnel barrier region130 may be formed as a single monolayer.

The fixed region 110 exhibits a magnetic orientation that is at leastsubstantially fixed, while the free region 120 exhibits a magneticorientation that is switchable. With reference to FIG. 1A, in someembodiments, an MTJ 100A may be configured for an out-of-plane STT-MRAMcell. Thus, the fixed region 110 exhibits an at least substantiallyfixed vertical magnetic orientation, as indicated by arrows 112A, whilethe free region 120 exhibits a switchable vertical magnetic orientation,as indicated by arrows 122A. With reference to FIG. 1B, in otherembodiments, an MTJ 100B may be configured for an in-plane STT-MRAMcell. Thus, the fixed region 110 exhibits an at least substantiallyfixed horizontal magnetic orientation, as indicated by arrows 112B,while the free region 120 exhibits a switchable horizontal magneticorientation, as indicated by arrows 122B.

The MTJ 100 of FIG. 1, and of any other embodiment disclosed herein, maybe configured to have an aligned lattice microstructure, as illustratedin FIG. 2. FIG. 2 illustrates, in simplified form, the atomic bonds ofan example crystal structure about an interface between a magneticmaterial 210 of the fixed region 110 (FIG. 1) and a nonmagnetic material230 of the tunnel barrier region 130 and about an interface between thenonmagnetic material 230 and another magnetic material 220 of the freeregion 120 (FIG. 1). The illustrated aligned lattice microstructure maybe substantially consistent across a width of the materials. That is,the structure illustrated in FIG. 2. may be repeated across the width ofthe materials.

The nonmagnetic material 230 may be bonded with each of the magneticmaterial 210 and the another magnetic material 220 by inter-materialbonds that span the respective interface. Each of the magnetic material210, the nonmagnetic material 230, and the another magnetic material 220may exhibit a crystal structure in the same geometric crystal system(e.g., a hexagonal crystal structure).

In one particular example, according to an embodiment of the presentdisclosure, the magnetic material 210 and the another magnetic material220 may both comprise, consist essentially of, or consist of hexagonalcobalt (h-Co), and the nonmagnetic material 230 may comprise, consistessentially of, or consist of hexagonal boron nitride (h-BN). The h-Coand the h-BN may have matching crystal structures, e.g., matchinghexagonal (0001) crystal structures. The a-lattice length of h-Co may beabout 2.5 Å (e.g., about 2.51 Å), and the a-lattice length of the h-BNmay also be about 2.5 Å (e.g., about 2.51 Å).

The h-Co of the magnetic material 210 and the another magnetic material220 may exhibit a hexagonal close-packed (hcp) crystal structure, e.g.,an hcp (0001) crystal structure. Thus, as illustrated in FIG. 2, levelsof h-Co in the magnetic material 210 and the another magnetic material220 are offset from one another as they alternate, with a cobalt atom ofa lower level laterally between cobalt atoms of an upper level.

The h-BN of the nonmagnetic material 230 may not exhibit a close-packstructure (e.g., an hcp structure), but may nonetheless exhibit ahexagonal (0001) crystal structure. Thus, the basal surface (i.e., thehexagonal face) of the h-BN may be exposed to the magnetic material andto the another magnetic material 220. The hexagonal ring of h-BN isdefined by atoms of boron alternating with atoms of nitrogen about thering, with each atom of boron bonded to two neighboring nitrogen atoms,and vice versa. The atoms of boron and atoms of nitrogen may alsoalternate through the levels of the h-BN lattice, with each atom ofboron bonded to two atoms of nitrogen, above and below, and vice versa.

In the aligned lattice microstructure of the MTJ 100, the basal surface(i.e., the hexagonal face) of each of the h-Co and the h-BN may besubstantially parallel with one another and with the interfaces definedbetween the materials. At the interfaces, each nitrogen (N) atom of theh-BN hexagonal face may bond with a cobalt (Co) atom of the periphery ofthe hexagonal face of the h-Co. This pattern may be substantiallyconsistent across the interfaces, to define the aligned latticemicrostructure in the MTJ 100.

The matching crystal structures of the materials of the MTJ 100 (e.g.,the magnetic material 210, the another magnetic material 220, and thenonmagnetic material 230) and the alignment between the materials in thealigned lattice microstructure may enable the MTJ 100 to exhibit a highTMR. The h-Co|h-BN|h-Co aligned lattice microstructure may also enablethe MTJ 100 to exhibit other desirable characteristics for a magneticcell, such as low damping and high MA strength. Low damping may enableuse of a low programming current during programming of the cell, and thehigh MA strength may inhibit the cell from prematurely switching, e.g.,during storage.

To form the materials of the MTJ 100 with the desired crystal structure(e.g., a hexagonal crystal structure, e.g., a hexagonal (0001) crystalstructure) and in the aligned lattice microstructure, the MTJ 100 may beformed proximate to a seed material, which may have a “desired crystalstructure,” i.e., a crystal structure matching that of the crystalstructure of the adjoining magnetic material (e.g., the magneticmaterial 210 or the another magnetic material 220) in the MTJ 100. Theproximity of the MTJ 100 to the seed material may enable the seedmaterial's crystal structure to effect the crystal structure in thematerials of the MTJ 100. For example, the materials of the MTJ 100 maybe formed (e.g., sputtered) over the seed material having the desiredcrystal structure, with the materials templating to the underlying seedmaterial. Thus, the crystal structure in the materials of the MTJ 100may be epitaxially grown from the seed material's desired crystalstructure. Alternatively, or additionally, the materials of the MTJ 100may be formed (e.g., sputtered) with a precursor microstructure (e.g.,an amorphous microstructure) and later converted (e.g., duringannealing) to the desired crystal structure through solid phase epitaxy,i.e., through propagation of the desired crystal structure from the seedmaterial. In such embodiments, the seed material may be under, over, orboth under and over the materials of the MTJ 100.

In one particular example, in embodiments in which the MTJ 100 is formedwith an h-Co|h-BN|h-Co aligned lattice microstructure (e.g., as in FIG.2), in which the magnetic material 210 of the fixed region 110 is h-Cowith a hexagonal (0001) crystal structure, the nonmagnetic material 230of the tunnel barrier region 130 is h-BN with the hexagonal (0001)crystal structure, and the another magnetic material 220 of the freeregion 120 is h-Co with the hexagonal (0001) crystal structure, the seedmaterial (e.g., hexagonal zinc (h-Zn), hexagonal ruthenium (h-Ru)) mayexhibit the hexagonal (0001) crystal structure such that its basalsurface is substantially parallel with the basal surfaces of the h-Coand h-BN.

The seed material may be selected such that its crystal structure andlowest energy surface matches that of the materials of the MTJ 100 andsuch that the seed material's lattice length (e.g., its a-axis latticelength) differs only minimally (e.g., less than about 10% difference,e.g., less than about 6% difference, e.g., about 5% or less difference)from the corresponding lattice length (e.g., the a-axis lattice length)of the materials of the MTJ 100. For example, h-Zn (0001) has an a-axislattice length of about 2.66 Å, which differs from the correspondinga-axis lattice length of the h-Co (i.e., about 2.51 Å) by less thanabout 6%. Because of the minimal difference in lattice lengths betweenthe seed material and the proximate material of the MTJ 100 (e.g., themagnetic material 210 or the another magnetic material 220), thematerials of the MTJ 100 may template on the crystal structure of theseed material without causing high residual strain in the crystalstructure of the MTJ 100. Therefore, the aligned lattice microstructure(see FIG. 2) of the MTJ 100 may be achieved free or substantially freeof defects in the microstructure, and the high TMR may be achieved.

Without being limited to any one particular theory, it is contemplatedthat the proximity of the seed material, having the desired crystalstructure, to the materials of the MTJ 100 enables formation of thematerials of the MTJ 100 with a more perfect crystal structure (i.e., acrystal structure with fewer structural defects) than would beachievable were the same MTJ 100 structure to be formed under influenceof a neighboring material having other than the desired crystalstructure. It is expected that, were the materials of the MTJ 100 to beformed on or otherwise under the influence of a neighboring regionhaving a different crystalline microstructure to the desired crystalstructure, or even an amorphous microstructure, the materials of the MTJ100 may be inhibited from exhibiting the desired crystal structure, orthe crystal structure or structures exhibited may include defects due,for example, to a mis-alignment between the materials of the MTJ 100 andthe neighboring material with the different crystal structure.Therefore, forming the MTJ 100 proximate to the seed material may enablethe aligned lattice microstructure with fewer defects in themicrostructure than may be achieved in the absence of the seed material.

To enable the seed material to exhibit the desired crystal structure(e.g., the hexagonal crystal structure, e.g., the hexagonal (0001)crystal structure), the seed material may be formed proximate to (e.g.,on) a “foundation material,” which may be configured to be amorphouswhen the seed material is formed proximate thereto.

In embodiments in which the seed material is formed on the amorphous,foundation material, the amorphous nature of the foundation material mayenable the seed material to adopt a preferential crystal structure.Because the seed material may be selected such that its preferentialcrystal structure is the desired crystal structure, forming the seedmaterial over the foundation material may enable the seed material to beinitially formed to exhibit the desired crystal structure. Without beinglimited to any particular theory, it is contemplated that, were the seedmaterial to be formed on a crystalline material having a crystalstructure other than the desired crystal structure, the seed materialmay template to the other crystal structure and not achieve the desiredcrystal structure. Therefore, forming the seed material on an amorphousfoundation material may enable the seed material to be formed to exhibitthe desired crystal structure, which enables the subsequent formation ofthe materials of the MTJ 100 to template to the desired crystalstructure of the seed material.

In some embodiments, the seed material may be formed over the materialsof the MTJ 100, and the desired crystal structure may be laterpropagated to the materials of the MTJ 100 through solid phase epitaxy.In such embodiments, the material of the MTJ 100 on which the seedmaterial is formed (e.g., the magnetic material 210 or the anothermagnetic material 220) may be formulated and configured to be initiallyamorphous. Thus, when the seed material is formed thereon, the seedmaterial may be formed in its preferential crystal structure, i.e., thedesired crystal structure. In such embodiments, the amorphous materialof the MTJ 100 adjacent the seed material may be characterized herein asa “precursor material.” Following formation of the seed material, withits desired crystal structure, on the precursor material of the MTJ 100,the desired crystal structure may be propagated from the seed materialto the precursor material to convert the precursor material into acrystalline material exhibiting the desired crystal structure. Theprecursor material may be formulated to be amorphous, when initiallyformed, due to inclusion of one or more additives in the precursormaterial, the presence of which effects the amorphous structure. Theadditives may diffuse out from the precursor material, e.g., during asubsequent anneal, while the desired crystal structure is propagatedfrom the seed material to crystallize the precursor material less theadditive or additives.

In other embodiments, the seed material may overlay the MTJ 100 with anintermediate amorphous material (not illustrated) disposed between.Thus, the seed material may be formed to exhibit the desired crystalstructure upon formation. During a subsequent anneal, the desiredcrystal structure may be propagated to both the intermediate amorphousmaterial and the material of the MTJ 100 adjacent to the intermediatenow-crystalline material.

In any case, the proximity of the crystalline seed material to thematerials of the MTJ 100, whether the seed material is under, over, orboth under and over, the materials of the MTJ 100, enables the materialsof the MTJ 100 to be formed, either initially or through propagation,with a desired crystal structure. Thus, the materials of the MTJ 100,having corresponding crystal structures, may be formed to exhibit analigned lattice microstructure (see FIG. 2) that enables a high TMR.

With reference to FIGS. 3 through 8, illustrated are various embodimentsof magnetic cell structures including the MTJ 100 of FIG. 1. Withreference to FIG. 3, the MTJ 100 is included in a magnetic cellstructure 300 configured for a “top-pinned” magnetic memory cell with asingle seed region 180 underlying the MTJ 100. The magnetic cellstructure 300 includes a magnetic cell core 301 over a substrate 102.The magnetic cell core 301 may be disposed between an upper electrode104 above and a lower electrode 105 below.

The magnetic cell core 301 includes the MTJ 100, with the fixed region110, the free region 120, and the nonmagnetic, tunnel barrier region 130between.

Adjacent the fixed region 110 may be another magnetic region, e.g., a“reference region” 117. The reference region 117 may be configured toinclude a synthetic antiferromagnet (SAF) structure comprising, forexample and without limitation, magnetic sub-regions 118 alternatingwith conductive sub-regions 119 above and below a coupler sub-region115. The conductive sub-regions 119 may cause the magnetic sub-regions118 to exhibit a perpendicular magnetic orientation (e.g., the fixedvertical magnetic orientation 112A of FIG. 1A), while the couplersub-region 115 may be formulated and positioned to enable anti-parallelcoupling of the magnetic sub-regions 118 adjacent to the couplersub-region 115.

In other embodiments, the magnetic cell core 300 includes the fixedregion 110 without an adjacent reference region (e.g., without thereference region 117).

As illustrated in FIG. 3, the free region 120 may be formed proximate to(e.g., over) a seed region 180, which may be formed proximate to (e.g.,over) a foundation region 160. The seed region 180 is formed from theseed material described above. Therefore, the seed region 180 exhibits adesired crystal structure (e.g., a hexagonal crystal structure (e.g., ahexagonal (0001) crystal structure)).

The foundation region 160 is formed from the foundation materialdescribed above. Therefore, the foundation region 160 is amorphous, andit may be formed over (e.g., directly over) the lower electrode 105. Asillustrated in FIG. 3, in some embodiments, the foundation region 160may be configured to be a sub-region of the lower electrode 105. In suchembodiments, the foundation region 160 may be formed of an amorphousconductive material, e.g., a metallic glass, e.g., a boron rutheniumtungsten (BRuW) alloy, a ruthenium tungsten (RuW) alloy, a binarymetallic. The conductive material of the foundation region 160 may allowprogramming current to pass through the magnetic cell core 301 withoutsubstantial electrical resistance in the foundation region 160.Moreover, as described above, the amorphous nature of the foundationregion 160 may enable the seed material of the seed region 180 to beformed to exhibit its preferential crystal structure, which is thedesired crystal structure for the materials of the MTJ 100.

The thickness of each of the foundation region 160 and the seed region180 may be selected to provide the sufficient surface on which to formoverlying materials. For example, and without limitation, the foundationregion 160 may be about one nanometer (about 1 nm) to about tennanometers (about 10 nm) in thickness, while the seed region 180 may beabout one nanometer about 1 nm) to about ten nanometers (about 10 nm) inthickness.

One or more upper intermediary regions 150 may, optionally, be disposedover the magnetic regions of the magnetic cell structure 300. The upperintermediary regions 150, if included, may be configured to inhibitdiffusion of species between the upper electrode 104 and the materialsof the reference region 117. Alternatively or additionally, the upperintermediary regions 150 may include materials configured to act as etchstops during subsequent patterning processes.

Accordingly, disclosed is a memory cell comprising a magnetic cell core.The magnetic cell core comprises a magnetic region exhibiting ahexagonal crystal structure and another magnetic region exhibiting thehexagonal crystal structure. A tunnel barrier region is disposed betweenthe magnetic region and the another magnetic region. The tunnel barrierregion exhibits another hexagonal crystal structure. A seed region isproximate to at least one of the magnetic region and the anothermagnetic region, and the seed region exhibits a hexagonal crystalstructure matching the hexagonal crystal structure of the at least oneof the magnetic region and the another magnetic region.

With reference to FIG. 4, illustrated is a magnetic cell structure 400including the MTJ 100 and configured for a “bottom-pinned” magneticmemory cell with a single seed region (e.g., the seed region 180)underlying the MTJ 100. A magnetic cell core 401 of the magnetic cellstructure 400 includes the MTJ 100 over the seed region 180, which isover the foundation region 160. The seed region 180 and the foundationregion 160 may be disposed between the fixed region 110 and thereference region 117.

According to the embodiment of FIG. 4, the foundation region 160 may beamorphous and enable formation of the seed region 180 over thefoundation region 160 with the desired crystal structure. The magneticmaterial 210 (FIG. 2) of the fixed region 110 may then be formed on theseed region 180, templating on the desired crystal structure. Likewise,the nonmagnetic material 230 (FIG. 2) of the tunnel barrier region 130may be formed to template on the desired crystal structure of the fixedregion 110, and the another magnetic material 220 (FIG. 2) of the freeregion 120 may be formed to template on the desired crystal structure ofthe tunnel barrier region 130. Therefore, the MTJ 100 with the desiredcrystal structure (e.g., a hexagonal crystal structure (e.g., ahexagonal (0001) crystal structure)) may be formed due to the formationof the MTJ 100 over the material of the seed region 180.

As illustrated in FIG. 4, the magnetic cell structure 400 may,optionally, include lower intermediary regions 140 disposed under themagnetic regions (e.g., the free region 120, the fixed region 110, andthe reference region 117). The lower intermediary regions 140, ifincluded, may be configured to inhibit diffusion of species between thelower electrode 105 and overlying materials during operation of thememory cell.

With reference to FIG. 5, illustrated is a magnetic cell structure 500including the MTJ 100 and configured for a “top-pinned” magnetic memorycell with a single seed region (e.g., the seed region 180) overlying theMTJ 100. The seed region 180 may be included, in a magnetic cell core501 of the magnetic cell structure 500, between the fixed region 110 andthe reference region 117.

Optionally, an amorphous foundation region (e.g., the foundation region160 of FIG. 4) may be included between the seed region 180 and themagnetic material 210 (FIG. 2) of the fixed region 110 to enable theseed material of the seed region 180 to be formed at the desired crystalstructure. Alternatively, for example, the magnetic material 210 (FIG.2) of the fixed region 110 may be formed from a precursor material thatis amorphous so that the seed region 180 may be formed having thedesired crystal structure. The desired crystal structure may bepropagated to the precursor material to convert the material of thefixed region 110 to the desired crystal structure. The desired crystalstructure may continue to propagate down through the tunnel barrierregion 130 and the free region 120 of the MTJ 100 to ensure thematerials of the MTJ 100 all have matching crystal structures.

With reference to FIG. 6, illustrated is a magnetic cell structure 600with a magnetic cell core 601 including the MTJ 100 and configured for a“bottom-pinned” magnetic memory cell with a single seed region (e.g.,the seed region 180) overlying the MTJ 100. The seed region 180 may bedisposed between the free region 120 and the upper electrode 104.Optionally, one or more upper intermediary regions 150 (see FIG. 5) maybe included between the upper electrode 104 and the seed region 180.

Optionally, an amorphous foundation region (e.g., the foundation region160 of FIG. 4) may be disposed between the seed region 180 and the freeregion 120 to enable the seed region 180 to be formed at the desiredcrystal structure, i.e., its preferential crystal structure.Alternatively, the magnetic material of the free region 120 may beformed from an amorphous precursor material to the another magneticmaterial 220 (FIG. 2) of the free region 120. The desired crystalstructure of the seed region 180 may be propagated down throughamorphous precursor material and the other materials of the MTJ 100during subsequent processing (e.g., during an anneal) to enable thematerials of the MTJ 100 to have crystal structures matching the desiredcrystal structure and one another.

With reference to FIG. 7, illustrated is a magnetic cell structure 700with a magnetic cell core 701 including the MTJ 100 and configured for a“top-pinned” magnetic memory cell with dual seed regions, i.e., the seedregion 180 and another seed region 780, below and above, respectively,the MTJ 100. The seed region 180 may be disposed on an amorphousfoundation region 160, which may enable the seed region 180 to be formedat the desired crystal structure. The another seed region 780 may bedisposed between the fixed region 110 and the reference region 117.

With dual seed regions (i.e., the seed region 180 and the another seedregion 780), the desired crystal structure may be promoted from bothbelow and above the MTJ 100. For example, the seed region 180,underlying the MTJ 100, may enable the another magnetic material 220(FIG. 2) of the free region 120 to form, by epitaxial crystal growth,the desired crystal structure exhibited by the seed region 180. Thetunnel barrier region 130 may form, also by epitaxial crystal growth,the desired crystal structure of the free region 120. The fixed region110 may form, by epitaxial crystal growth, the desired crystal structureof the tunnel barrier region 130. Moreover, during a subsequent anneal,the desired crystal structure exhibited by the another seed region 780may be propagated downward, by solid phase epitaxy, into the MTJ 100 tofurther promote the crystal structure exhibited by materials of the MTJ100.

The seed material of the seed region 180 and the another seed region 780may be the same or different materials. However, it is contemplated thatthe seed materials, whether the same or different, be selected toexhibit the desired crystal structure to enable formation of the MTJ 100with the aligned lattice microstructure. Thus, high TMR and otherdesirable characteristics (e.g., high MA strength and low damping) maybe achieved.

With reference to FIG. 8, illustrated is a magnetic cell structure 800having a magnetic cell core 801 that includes the MTJ 100 and configuredfor a “bottom-pinned” magnetic memory cell with dual seed regions, e.g.,the seed region 180 and the another seed region 780, below and above,respectively, the MTJ 100. The seed region 180 may be disposed betweenthe fixed region 110 and the reference region 117. The amorphousfoundation region 160 may be between the seed region 180 and thereference region 117.

As with the embodiment of FIG. 7, the dual seed regions may promote thedesired crystal structure in the MTJ 100 from both above and below. Theseed region 180, below the MTJ 100, may enable templating of the desiredcrystal structure as the materials of the MTJ 100 are initially formed,e.g., by epitaxial crystal growth, while the another seed region 780,above the MTJ 100, may enable propagation of the desired crystalstructure, e.g., by solid phase epitaxy, downward into the materials ofthe MTJ 100, such as during a subsequent anneal.

In any of the foregoing magnetic cell structures 300 (FIG. 3), 400 (FIG.4), 500 (FIG. 5), 600 (FIG. 6), 700 (FIG. 7), 800 (FIG. 8), the MTJ 100may he formed as an h-Co|h-BN|h-Co aligned lattice microstructure, andthe seed region 180 and, if present, the another seed region 780 may beformed of h-Zn or another conductive material having a crystal structurematching that of h-Co. Additionally, the foundation region 160, ifpresent, may be formed of an amorphous conductive material.

Accordingly, disclosed is a memory cell comprising a magnetic cell core.The magnetic cell core comprises a magnetic tunnel junction adjacent aseed region exhibiting a hexagonal crystal structure. The magnetictunnel junction comprises hexagonal boron nitride between hexagonalcobalt. An amorphous region is adjacent the seed region.

With reference to FIG. 9, illustrated is a stage in a method offabricating one or more magnetic cell structures (e.g., the magneticcell structure 300 of FIG. 3). A precursor structure 900, comprising asequence of materials, may be formed, in order, one material after theother, from the substrate 102 to an upper-most material. Accordingly,though the precursor structure 900 of FIG. 9 illustrates a sequence ofmaterials that corresponds to that for forming the magnetic cellstructure 300 of FIG. 3, it should be recognized that the order ofmaterials may be appropriately adjusted to correspond to that of any ofthe other magnetic cell structures 400 through 800 (FIGS. 4 through 8,respectively), disclosed herein.

Though the materials of the precursor structure 900 may be formed insequence, more than one formation technique may be utilized duringformation of the precursor structure 900. Accordingly, while one or morematerials may be formed by, e.g., sputtering, one or more othermaterials may be formed by other techniques, such as, and withoutlimitation, laser ablation, ALD, or CVD. The formation technique may beselected in light of the material to be formed.

A conductive material 905 may be formed over the substrate 102. Theconductive material 905, from which the lower electrode 105 (FIGS. 3through 8) is to be formed, may comprise, consist essentially of, orconsist of, for example and without limitation, a metal (e.g., copper,tungsten, titanium, tantalum), a metal alloy, or a combination thereof.

In embodiments in which the optional lower intermediary region 140(FIGS. 4, 5, 6, and 8) may, optionally, be formed over the lowerelectrode 105, one or more lower intermediary materials (not illustratedin FIG. 9) may be formed over the conductive material 905. The lowerintermediary materials, from which the lower intermediary region 140 isformed, may comprise, consist essentially of, or consist of, for exampleand without limitation, tantalum (Ta), titanium (Ti), tantalum nitride(TaN), titanium nitride (TiN), ruthenium (Ru), tungsten (W), or acombination thereof. In some embodiments, the lower intermediarymaterial, if included, may be incorporated with the conductive material905 from which the lower electrode 105 (FIGS. 3 through 8) is to beformed. For example, the lower intermediary material may be anupper-most sub-region of the conductive material 905.

In embodiments to form the magnetic cell structures 300, 700 of FIGS. 3and 7, respectively, the foundation material described above (e.g., afoundation material 960) may be formed over the conductive material 905and the lower intermediary materials, if present. The foundationmaterial 960 may be amorphous and may comprise, consist essentially of,or consist of an amorphous conductive material, e.g., a metallic glass.The foundation material 960 may be formulated and configured to providean amorphous surface that enables forming a seed material 980 thereoverat a desired crystal structure (e.g., a hexagonal crystal structure,e.g., a hexagonal (0001) crystal structure). The seed material 980 maycomprise, consist essentially of, or consist of any of theabove-described seed materials (e.g., h-Zn (0001)).

In some embodiments, the seed material 980 may exhibit the desiredcrystal structure when initially formed on an underlying material. Inother embodiments, the seed material 980 may be formed from a precursorseed material that does not exhibit the desired crystal structure wheninitially formed. For example, the precursor seed material may beannealed at a temperature within about 10% below the melting temperatureof the precursor seed material, and the anneal may enable atoms of theprecursor seed material to align in the desired crystal orpolycrystalline structure having a desired crystal space group andorientation and to minimize overall system energy. Therefore, the seedmaterial 980, exhibiting the desired crystal structure (or desiredpolycrystalline structure) is formed from the precursor seed material.In embodiments in which the seed material 980 comprises, consistsessentially of, or consists of h-Zn, the precursor seed material maycomprise, consist essentially of, or consist of zinc (Zn), which has amelting temperature of about 419.5° C. Therefore, the Zn-based precursorseed material may be annealed at a temperature between about 377.5° C.and about 419.5° C. to form the h-Zn exhibiting a desired hexagonalcrystal structure and having the (0001) crystal plane as the crystalplane with the lowest surface energy.

The another magnetic material 220, from which the free region 120(FIG. 1) is to be formed, may be formed over the seed material 980, andmay be formulated and configured to template on the desired crystalstructure of the seed material 980. In embodiments in which the seedmaterial 980 exhibits the desired crystal structure as a result of ananneal, the another magnetic material 220 may be formed over the seedmaterial 980 after the seed material 980 has been annealed to exhibitthe desired crystal structure. In other embodiments, the anothermagnetic material 220 may be formed over the precursor seed materialprior to annealing the precursor seed material, and the desired crystalstructure, effected during the anneal of a precursor seed material, maypropagate to the another magnetic material 220.

The nonmagnetic material 230, from which the tunnel barrier region 130(FIG. 1) is to be formed, may be formed over the another magneticmaterial 220 and may be formulated and configured to template on thedesired crystal structure of the another magnetic material 220. Themagnetic material 210, from which the fixed region 110 (FIG. 1) is to beformed, may be formed over the nonmagnetic material 230 and may beformulated and configured to template on the desired crystal structureof the nonmagnetic material 230. The magnetic material 210 may be thesame as or a different material than the another magnetic material 220.Either or both of the magnetic material 210 and the another magneticmaterial 220 may be formed homogeneously or, optionally, may be formedto include sub-regions of different materials.

The materials of the reference region 117 (FIG. 3) may then be formedover the above-described structure. For example, magnetic material 918and conductive material 919 may be formed in an alternating structurewith a coupler material 915 disposed between an upper alternatingstructure and a lower alternating structure of the magnetic material 918and the conductive material 919. For example, and without limitation,the magnetic material 918 may comprise, consist essentially of orconsist of cobalt (Co); the conductive material 919 may comprise,consist essentially of, or consist of platinum (Pt); and the couplermaterial 915 may comprise, consist essentially of, or consist ofruthenium (Ru). In other embodiments, the materials of the referenceregion 117 (FIG. 3) may comprise, consist essentially of, or consist ofcobalt/palladium (Co/Pd) multi-sub-regions; cobalt/platinum (Co/Pt)multi-sub-regions; cobalt/nickel (Co/Ni) multi-sub-regions;cobalt/iridium (Co/Ir) multi-sub-regions; cobalt iron terbium (Co/Fe/Tb)based materials, L₁0 materials, coupler materials, or other magneticmaterials of conventional fixed regions.

In some embodiments, optionally, one or more upper intermediarymaterials 950 may be formed over the materials for the reference region117 (FIG. 3). The upper intermediary materials 950, which, if included,form the optional upper intermediary regions 150 (FIG. 3), may comprise,consist essentially of, or consist of materials configured to ensure adesired crystal structure in neighboring materials. The upperintermediary materials 950 may alternatively or additionally includemetal materials configured to aid in patterning processes duringfabrication of the magnetic cell, barrier materials, or other materialsof conventional STT-MRAM cell core structures. In some embodiments, theupper intermediary material 950 may include a conductive material (e.g.,one or more materials such as copper, tantalum, titanium, tungsten,ruthenium, tantalum nitride, or titanium nitride) to be formed into aconductive capping region.

Another conductive material 904, from which the upper electrode 104(FIG. 3) may be formed, may be formed over the materials for thereference region 117 (FIG. 3) and, if present, the upper intermediarymaterials 950. In some embodiments, the another conductive material 904and the upper intermediary materials 950, if present, may be integratedwith one another, e.g., with the upper intermediary materials 950 beinglower sub-regions of the conductive material 904.

Some or all of the materials of the precursor structure 900 may beannealed, in one or more annealing stages, e.g., to promotecrystallization of materials. For example, in some embodiments, thematerials of lower segment 9A of FIG. 9 may be formed and annealed toenable or improve the crystal structure of the seed material 980 intothe desired crystal structure. Thereafter, the materials of middlesegment 9B of FIG. 9, i.e., the materials of the MTJ 100 (FIG. 1), maybe formed, in sequence, over the seed material 980. In some embodiments,forming the materials of the middle segment 9B may enable the materialsto exhibit the desired crystal structure by templating on the seedmaterial 980. Subsequent annealing of both the lower segment 9A with themiddle segment 9B may improve the crystal structure in the materials ofthe MTJ 100 as well as improve the alignment of the latticemicrostructures in the MTJ 100.

In embodiments in which the materials of the MTJ 100, formed over theseed material 980, do not initially template on the desired crystalstructure exhibited by the seed material 980, subjecting the lowersegment 9A and the middle segment 9B to an anneal may propagate thedesired crystal structure from the seed material 980 to the materials ofthe MTJ 100 by solid phase epitaxy.

The materials of upper segment 9C may then be formed over the middlesegment 9B and, optionally, subjected to another anneal.

Though three anneal stages are described with respect to the formationof the precursor structure of FIG. 9, it is contemplated that feweranneals or additional anneals may, alternatively, be utilized.

Because the seed material 980 may be subjected to one or more anneals,the seed material 980 may be formulated or otherwise selected to have amelting temperature that is higher than the anneal temperature to beused. For example, the seed material 980 may be h-Zn with a meltingtemperature of approximately 420° C., and the anneal temperaturessubsequently used may be lower than about 400° C., e.g., about 250° C.

Because, at least in some embodiments, the materials of the MTJ 100(e.g., the magnetic material 210, the another magnetic material 220, andthe nonmagnetic material 230) may not be formulated to include additivesthat are to out-diffuse during anneal, the degradation ofcharacteristics (e.g., in magnetic anisotropy (“MA”) strength) caused byout-diffusion of such additives in conventional magnetic cell structuresmay be avoided.

The seed material 980 is formed to at least cover region 9D of FIG. 9.Region 9D is the region to be occupied by a magnetic cell core structure(e.g., the magnetic cell core structure 300 of FIG. 3). In someembodiments, such as that of FIG. 9, the seed material 980 may cover theentirety of an upper surface of its neighboring, underlying material(e.g., the foundation material 960). In other embodiments, the seedmaterial 980 may be formed to cover substantially only region 9D. In anycase, the seed material 980 exhibits the desired crystal structure, andthe overlying materials of the MTJ 100 may be formed to template fromthe desired crystal structure.

In embodiments in which the seed material 980 extends over more thanjust region 9D, the seed material 980 is monocrystalline, exhibiting thedesired crystal structure, in region 9D. In some embodiments, the seedmaterial 980 may be monocrystalline across its entire width. In otherembodiments, the seed material 980 exhibit a different crystal structure(e.g., a polycrystalline structure) in regions adjacent to the region9D. In any case, the seed material 980 exhibits the desired crystalstructure (e.g., a hexagonal crystal structure) in the region 9D wherethe magnetic cell core (e.g., the magnetic cell core 301 of FIG. 3) isto be formed. The exhibition of other crystal structures, by the seedmaterial 980, in regions substantially external to region 9D may not bedetrimental, provided the adjacent material of the MTJ 100 (FIG. 1) maybe formed to exhibit, throughout its width in region 9D, a matchingcrystal structure to the desired crystal structure of the seed material980, whether by templating (i.e., epitaxial crystal growth) or bypropagation (i.e., solid phase epitaxy), and also provided that theother materials of the MTJ 100 (FIG. 1) may be formed to, likewise,exhibit matching crystal structures, in the aligned latticemicrostructure, throughout the width of region 9D.

The precursor structure 900 may be patterned, in one or more stages, toform the magnetic cell structure (e.g., the magnetic cell structure 300of FIG. 3). Techniques for patterning structures such as the precursorstructure 900 to form structures such as the magnetic cell structure 300(FIG. 3) are known in the art and so are not described herein in detail.

Accordingly, disclosed is a method of forming a memory cell. The methodcomprises forming a seed material over a substrate. The seed materialexhibits a hexagonal crystal structure. Materials of a magnetic tunneljunction are formed proximate to the seed material to effect, by atleast one of epitaxial crystal growth and solid phase epitaxy, thehexagonal crystal structure in the materials. Forming the materials ofthe magnetic tunnel junction comprises forming a magnetic material,forming a nonmagnetic material on the magnetic material, and forminganother magnetic material on the nonmagnetic material.

Also disclosed is a method of forming a memory cell, comprising forminga precursor structure over a substrate. Forming the precursor structurecomprises forming an amorphous material over the substrate, forming aseed material over the amorphous material, forming a magnetic materialon the seed material, forming a nonmagnetic material over the magneticmaterial, and forming another magnetic material over the nonmagneticmaterial. The seed material exhibits a hexagonal crystal structure. Theprecursor structure is patterned to form a magnetic cell core.

With reference to FIG. 10, illustrated is an STT-MRAM system 1000 thatincludes peripheral devices 1012 in operable communication with anSTT-MRAM cell 1014, a grouping of which may be fabricated to form anarray of memory cells in a grid pattern including a number of rows andcolumns, or in various other arrangements, depending on the systemrequirements and fabrication technology. The STT-MRAM cell 1014 includesa magnetic cell core 1002, an access transistor 1003, a conductivematerial that may function as a data/sense line 1004 (e.g., a bit line),a conductive material that may function as an access line 1005 (e.g., aword line), and a conductive material that may function as a source line1006. The peripheral devices 1012 of the STT-MRAM system 1000 mayinclude read/write circuitry 1007, a bit line reference 1008, and asense amplifier 1009. The cell core 1002 may be any one of the magneticcell cores (e.g., the magnetic cell cores 301 through 801 (FIGS. 3through 8) described above. Due to the structure of the cell core 1002,the method of fabrication, or both, the STT-MRAM cell 1014 may have ahigh TMR.

In use and operation, when the STT-MRAM cell 1014 is selected to beprogrammed, a programming current is applied to the STT-MRAM cell 1014,and the current is spin-polarized by the fixed region 110 (FIG. 1) ofthe cell core 1002 and exerts a torque on the free region 120 (FIG. 1)of the cell core 1002, which switches the magnetization of the freeregion 120 to “write to” or “program” the STT-MRAM cell 1014. In a readoperation of the STT-MRAM cell 1014, a current is used to detect theresistance state of the cell core 1002.

To initiate programming of the STT-MRAM cell 1014, the read/writecircuitry 1007 may generate a write current (i.e., a programmingcurrent) to the data/sense line 1004 and the source line 1006. Thepolarity of the voltage between the data/sense line 1004 and the sourceline 1006 determines the switch in magnetic orientation of the freeregion 120 (FIG. 1) in the cell core 1002. By changing the magneticorientation of the free region 120 with the spin polarity, the freeregion 120 is magnetized according to the spin polarity of theprogramming current, the programmed logic state is written to theSTT-MRAM cell 1014.

To read the STT-MRAM cell 1014, the read/write circuitry 1007 generatesa read voltage to the data/sense line 1004 and the source line 1006through the cell core 1002 and the access transistor 1003. Theprogrammed state of the STT-MRAM cell 1014 relates to the electricalresistance across the cell core 1002, which may be determined by thevoltage difference between the data/sense line 1004 and the source line1006. In some embodiments, the voltage difference may be compared to thebit line reference 1008 and amplified by the sense amplifier 1009.

FIG. 10 illustrates one example of an operable STT-MRAM system 1000. Itis contemplated, however, that the magnetic cell cores 301 through 801(FIGS. 3 through 8) may be incorporated and utilized within any STT-MRAMsystem configured to incorporate a magnetic cell core having magneticregions.

Accordingly, disclosed is a semiconductor device comprising a spintorque transfer magnetic random memory (STT-MRAM) array comprisingSTT-MRAM cells. At least one STT-MRAM cell of the STT-MRAM cellscomprises a magnetic tunnel junction comprising a free region, a tunnelbarrier region, and a fixed region. The free region comprises hexagonalcobalt, the tunnel barrier region comprises hexagonal boron nitride, andthe fixed region comprises hexagonal cobalt. A conductive seed region isadjacent the magnetic tunnel junction. The conductive seed regioncomprises a hexagonal crystal structure.

With reference to FIG. 11, illustrated is a simplified block diagram ofa semiconductor device 1100 implemented according to one or moreembodiments described herein. The semiconductor device 1100 includes amemory array 1102 and a control logic component 1104. The memory array1102 may include a plurality of the STT-MRAM cells 1014 (FIG. 10)including any of the magnetic cell cores 301 through 801 (FIGS. 3through 8) discussed above, which magnetic cell cores 301 through 801(FIGS. 3 through 8) may have been formed according to a method describedabove and may be operated according to a method described above. Thecontrol logic component 1104 may be configured to operatively interactwith the memory array 1102 so as to read from or write to any or allmemory cells (e.g., STT-MRAM cell 1014 (FIG. 10)) within the memoryarray 1102.

With reference to FIG. 12, depicted is a processor-based system 1200.The processor-based system 1200 may include various electronic devicesmanufactured in accordance with embodiments of the present disclosure.The processor-based system 1200 may be any of a variety of types such asa computer, pager, cellular phone, personal organizer, control circuit,or other electronic device. The processor-based system 1200 may includeone or more processors 1202, such as a microprocessor, to control theprocessing of system functions and requests in the processor-basedsystem 1200. The processor 1202 and other subcomponents of theprocessor-based system 1200 may include magnetic memory devicesmanufactured in accordance with embodiments of the present disclosure.

The processor-based system 1200 may include a power supply 1204 inoperable communication with the processor 1202. For example, if theprocessor-based system 1200 is a portable system, the power supply 1204may include one or more of a fuel cell, a power scavenging device,permanent batteries, replaceable batteries, and rechargeable batteries.The power supply 1204 may also include an AC adapter; therefore, theprocessor-based system 1200 may be plugged into a wall outlet, forexample. The power supply 1204 may also include a DC adapter such thatthe processor-based system 1200 may be plugged into a vehicle cigarettelighter or a vehicle power port, for example.

Various other devices may be coupled to the processor 1202 depending onthe functions that the processor-based system 1200 performs. Forexample, a user interface 1206 may be coupled to the processor 1202. Theuser interface 1206 may include input devices such as buttons, switches,a keyboard, a light pen, a mouse, a digitizer and stylus, a touchscreen, a voice recognition system, a microphone, or a combinationthereof. A display 1208 may also be coupled to the processor 1202. Thedisplay 1208 may include an LCD display, an SED display, a CRT display,a DLP display, a plasma display, an OLED display, an LED display, athree-dimensional projection, an audio display, or a combinationthereof. Furthermore, an RF sub-system/baseband processor 1210 may alsobe coupled to the processor 1202. The RF sub-system/baseband processor1210 may include an antenna that is coupled to an RF receiver and to anRF transmitter (not shown). A communication port 1212, or more than onecommunication port 1212, may also be coupled to the processor 1202. Thecommunication port 1212 may be adapted to be coupled to one or moreperipheral devices 1214, such as a modem, a printer, a computer, ascanner, or a camera, or to a network, such as a local area network,remote area network, intranet, or the Internet, for example.

The processor 1202 may control the processor-based system 1200 byimplementing software programs stored in the memory. The softwareprograms may include an operating system, database software, draftingsoftware, word processing software, media editing software, or mediaplaying software, for example. The memory is operably coupled to theprocessor 1202 to store and facilitate execution of various programs.For example, the processor 1202 may be coupled to system memory 1216,which may include one or more of spin torque transfer magnetic randomaccess memory (STT-MRAM), magnetic random access memory (MRAM), dynamicrandom access memory (DRAM), static random access memory (SRAM),racetrack memory, and other known memory types. The system memory 1216may include volatile memory, non-volatile memory, or a combinationthereof. The system memory 1216 is typically large so that it can storedynamically loaded applications and data. In some embodiments, thesystem memory 1216 may include semiconductor devices, such as thesemiconductor device 1100 of FIG. 11, memory cells including any of themagnetic cell cores 301 through 801 (FIGS. 3 through 8) described above,or a combination thereof.

The processor 1202 may also be coupled to non-volatile memory 1218,which is not to suggest that system memory 1216 is necessarily volatile.The non-volatile memory 1218 may include one or more of STT-MRAM, MRAM,read-only memory (ROM) such as an EPROM, resistive read-only memory(RROM), and flash memory to be used in conjunction with the systemmemory 1216. The size of the non-volatile memory 1218 is typicallyselected to be just large enough to store any necessary operatingsystem, application programs, and fixed data. Additionally, thenon-volatile memory 1218 may include a high capacity memory such as diskdrive memory, such as a hybrid-drive including resistive memory or othertypes of non-volatile solid-state memory, for example. The non-volatilememory 1218 may include semiconductor devices, such as the semiconductordevice 1100 of FIG. 11, memory cells including any of the magnetic cellcores 301 through 801 (FIGS. 3 through 8) described above, or acombination thereof.

While the present disclosure is susceptible to various modifications andalternative fauns in implementation thereof, specific embodiments havebeen shown by way of example in the drawings and have been described indetail herein. However, the present disclosure is not intended to belimited to the particular forms disclosed. Rather, the presentdisclosure encompasses all modifications, combinations, equivalents,variations, and alternatives falling within the scope of the presentdisclosure as defined by the following appended claims and their legalequivalents.

What is claimed is:
 1. A memory cell, comprising: a magnetic cell corecomprising: a magnetic region exhibiting a hexagonal crystal structure;another magnetic region exhibiting the hexagonal crystal structure; atunnel barrier region between the magnetic region and the anothermagnetic region, the tunnel barrier region exhibiting another hexagonalcrystal structure; and a seed region proximate to at least one of themagnetic region and the another magnetic region, the seed regionexhibiting a hexagonal crystal structure matching the hexagonal crystalstructure of the at least one of the magnetic region and the anothermagnetic region.
 2. The memory cell of claim 1, wherein: the magneticregion comprises hexagonal cobalt; the another magnetic region compriseshexagonal cobalt; and the tunnel barrier region comprises hexagonalboron nitride.
 3. The memory cell of claim 1, wherein the seed regioncomprises hexagonal zinc.
 4. The memory cell of claim 1, furthercomprising another seed region proximate to at least another of themagnetic region and the another magnetic region, the another seed regionexhibiting a hexagonal crystal structure matching the hexagonal crystalstructure of the another of the magnetic region and the another magneticregion.
 5. The memory cell of claim 1, wherein the seed region isdisposed between a reference region and the at least one of the magneticregion and the another magnetic region.
 6. A memory cell, comprising: amagnetic cell core comprising: a magnetic tunnel junction adjacent aseed region exhibiting a hexagonal crystal structure, the magnetictunnel junction comprising hexagonal boron nitride between hexagonalcobalt; and an amorphous region adjacent the seed region.
 7. The memorycell of claim 6, wherein the amorphous region is disposed between theseed region and a lower electrode.
 8. The memory cell of claim 7,wherein the amorphous region comprises a metallic glass.
 9. The memorycell of claim 6, wherein the seed region is disposed above the magnetictunnel junction.
 10. The memory cell of claim 6, wherein the seed regionis disposed below the magnetic tunnel junction.
 11. A method of forminga memory cell, comprising: forming a seed material over a substrate, theseed material exhibiting a hexagonal crystal structure; and formingmaterials of a magnetic tunnel junction proximate to the seed materialto effect, by at least one of epitaxial crystal growth and solid phaseepitaxy, the hexagonal crystal structure in the materials, comprising:forming a magnetic material; forming a nonmagnetic material on themagnetic material; and forming another magnetic material on thenonmagnetic material.
 12. The method of claim 11, wherein formingmaterials of a magnetic tunnel junction proximate to the seed materialcomprises forming the materials of the magnetic tunnel junction over theseed material to effect, by epitaxial crystal growth, the hexagonalcrystal structure in the materials of the magnetic tunnel junction. 13.The method of claim 11, wherein: forming the materials of the magnetictunnel junction precedes forming the seed material over the substrate;and forming the seed material over the substrate comprises forming theseed material over the substrate and on the materials of the magnetictunnel junction.
 14. The method of claim 13, wherein forming thematerials of the magnetic tunnel junction comprises propagating thehexagonal crystal structure from the seed material to the materials ofthe magnetic tunnel junction to effect, by solid phase epitaxy, thehexagonal crystal structure in the materials.
 15. A method of forming amemory cell, comprising: forming a precursor structure over a substrate,comprising: forming an amorphous material over the substrate; forming aseed material over the amorphous material, the seed material exhibitinga hexagonal crystal structure; forming a magnetic material on the seedmaterial, the magnetic material exhibiting a hexagonal crystal structurematching the hexagonal crystal structure of the seed material; forming anonmagnetic material over the magnetic material, the nonmagneticmaterial exhibiting another hexagonal crystal structure matching thehexagonal crystal structure of the magnetic material; and forminganother magnetic material over the nonmagnetic material, the anothermagnetic material exhibiting a hexagonal crystal structure matching theanother hexagonal crystal structure of the nonmagnetic material; andpatterning the precursor structure to form a magnetic cell core.
 16. Themethod of claim 15, further comprising annealing the precursor structureat a temperature less than a melting temperature of the seed material.17. The method of claim 16, wherein annealing the precursor structure ata temperature less than a melting temperature of the seed materialcomprises annealing at a temperature of less than about 300° C.
 18. Themethod of claim 15, wherein forming a precursor structure furthercomprises forming another seed material over the another magneticmaterial, the another seed material exhibiting the hexagonal crystalstructure of the seed material.
 19. A semiconductor device, comprising:a spin torque transfer magnetic random access memory (STT-MRAM) arraycomprising: SIT-MRAM cells, at least one STT-MRAM cell of the STT-MRAMcells comprising: a magnetic tunnel junction comprising: a free regioncomprising hexagonal cobalt; a tunnel barrier region comprisinghexagonal boron nitride; and a fixed region comprising hexagonal cobalt;and a conductive seed region adjacent the magnetic tunnel junction, theconductive seed region comprising a hexagonal crystal structure.
 20. Thesemiconductor device of claim 19, wherein the free region is disposedbelow the fixed region, the at least one STT-MRAM cell configured as atop-pinned magnetic memory cell.
 21. The semiconductor device of claim19, wherein the free region is disposed above the fixed region, the atleast one STT-MRAM cell configured as a bottom-pinned magnetic memorycell.
 22. The semiconductor device of claim 19, wherein the free regionand the fixed region exhibit vertical magnetic orientations.